Device for anchoring an endoprosthesis in a bone

ABSTRACT

A device is provided for anchoring an endoprosthesis in a bone, for example a thigh portion of a hip joint endoprosthesis in a femur. The device is configured in the form of a quiver-like receptacle which can be implanted in the bone for receiving a shaft of the endoprosthesis. The receptacle comprises an inner wall enclosing the shaft and an outer wall disposed at a distance therefrom. A space between the inner wall and the outer wall is filled with a medium, in which an externally applied pressure is uniformly distributed substantially to all sides for damping impacts exerted on the endoprosthesis.

CROSS REFERENCE TO PENDING APPLICATION

[0001] This application is a continuation of pending InternationalApplication PCT/EP99/04461 filed on Jun. 28, 1999, which designates theUnited States.

BACKGROUND OF THE INVENTION

[0002] The invention relates to a device for anchoring an endoprosthesisin a bone, for example a thigh portion of a hip joint endoprosthesis ina femur.

[0003] Endoprostheses are used in medicine to replace destroyed orirrepairably damaged parts of the human skeleton. In particular,endoprostheses are used as artificial replacements for joints,especially large joints such as the hip joint or the knee joint.Especially with a hip joint, the ball socket on the pelvis or the headincluding the neck of the femur or both can be replaced in the humanskeleton. Such total endoprosthetic systems generally have a shaft whichis implanted in the healthy bone structure of the skeletal part to bereplaced, while the neck and the head of the shaft extend from the bone.

[0004] The thigh portion of a hip joint endoprosthesis comprises anapproximately cylindrical, conical or also slightly curved shaft, whichhas a neck at its upper end and finally an artificial ball attachedthereto. The shaft of the thigh portion of such endoprostheses areinserted into the marrow cavity of the femur, which has been previouslyprepared.

[0005] For younger patients with sufficient bone substance capable ofgrowth, the endoprosthesis shaft is normally placed directly in theprepared marrow cavity, where the bone tissue next to the shaft growsonto the shaft. In older patients with complicated fractures of thecorresponding skeletal parts or with unstable bone substance, the shaftof the endoprosthesis is normally cemented into the narrow cavity. Insuch cases, particularly for older patients, sufficient bone tissuecapable of growth is no longer present to guarantee a reliable, stableanchoring of the shaft in the bone by growth of bone tissue onto theshaft.

[0006] Although considerable progress has been achieved in prostheticsurgery in the past three decades, a durable, stable anchoring of theprosthesis, free of abrasion and secured against release, has remained aproblem with endoprostheses implanted with or without cement.

[0007] Such endoprostheses are subject to large loads through movementof the prosthesis patient. For example, when descending a stairs forcesin the range of three to four times the body weight of the person areexerted on the thigh portion of the hip joint endoprosthesis. Theseforces act directly on the interface between the bone and endoprosthesisor between the cement and the endoprosthesis through the shaft.

[0008] The endoprosthesis shaft moves in the marrow cavity due to thechanging loads caused by the person moving. The shaft rubs against thesurface of the bone tissue or locally exerts forces on the bone tissue.Thus the growth of the bone onto the shaft is hindered or the bonetissue already grown or the cement deteriorates with time. A durable,stable anchoring of the endoprosthesis in the bone is endangered throughloads or peak loads, apart from rotational forces, which act not onlyvertically but in transverse direction to the endoprosthesis shaft. Thiscan cause excess loads on the bone-endoprosthesis interface or thecement-endoprosthesis interface either locally or at particular points,in particular in the region of the lower end of the shaft. The mentionedinterface is subjected to changing forces even with purely verticalloads on the endoprosthesis, which in time damage the interface. Thiscan lead to an osteologic reaction, which can result in a loosening ofthe endoprosthesis. Thus, a protection of the critical interface betweenthe bone and the endoprosthesis or between the cement and theendoprosthesis is decisive for the lifetime of the artificial joint.

[0009] From U.S. Pat. No. 4,892,550 an endoprosthesis device is knownwhich can be installed immovably in a medullary canal under a constantpredetermined uniformly distributed pressure. The rigid prosthesis shaftis typically embraced by an elastomeric element designed for continuouspressurization into compressed resilient anchorage with the medullarycanal surface. The tubular elastomeric element can be pressurized invarious ways, such as by a captive gas, or by a fluent material untilthis material takes a set, or by a combination of pressurized gas andsettable fluent material. The device for anchoring the shaft of theprosthesis in the bone is configured in quiver-like fashion. However,the captive gas or the fluent material is not present in the distal mostend region of the receptacle, where the receptacle is made from auniform material in one piece. Impacts vertically acting on theendoprosthesis cannot be damped sufficiently, with the risk that theendoprosthesis can axially further penetrate in the medullary canal.

[0010] The object of the invention is therefore to provide a durable,stable and non-releasable anchoring of an endoprosthesis in the boneinto which it is implanted.

SUMMARY OF THE INVENTION

[0011] According to the present invention, this object is achieved by adevice for anchoring an endoprosthesis in a bone, for example, a thighpart of a hip joint endoprosthesis in a femur, wherein the device isconfigured in form of a quiver-like receptacle implantable in the bonefor receiving a shaft of the endoprosthesis, the receptacle comprising:

[0012] an inner wall enclosing the shaft,

[0013] an outer wall disposed at a distance from the inner wall,

[0014] a medium filled in a space between the inner wall and the outerwall, in which medium an externally applied pressure is uniformlydistributed substantially to all sides for damping impacts exerted onthe endoprosthesis,

[0015] wherein the inner wall is disposed at a distance from the outerwall also at a distal most end of the receptacle.

[0016] The device of the present invention produces a mechanicaldecoupling of the shaft of the endoprosthesis from the tissue of thebone in which the endoprosthesis is implanted. With the device of thepresent invention, a particularly harmful momentum transfer from theshaft to the adjacent bone tissue or the cement is avoided. The shaft ofthe endoprosthesis is received in the quiver-like receptacle and liesagainst the inner wall of the receptacle. The separate outer wall of thequiver-like receptacle lies against the bone or the cement. When theendoprosthesis is subjected to a load, the resulting forces are dampenedby the medium present between the inner wall and the outer wall of thereceptacle, also at the distal most end between bottom portions of theouter and the inner wall, for example, dissipated. These forces aretransmitted to the bone tissue or the cement adjacent to the outer wall,but without strong impact or with distinctly reduced and distributedmomentum. The device according to the present invention thus acts as adamping buffer or a shock absorber between the shaft of theendoprosthesis and the adjacent bone tissue or cement. The outer wallwhich is in connection with the cement or the tissue of the bone is notdisturbed in this manner, so that no abrasion or friction occurs betweenthe outer wall and the adjacent cement or the bone tissue of the bone.The interface created between the outer wall of the receptacle and thecement or tissue is thus guarded against the alternating or fluctuatingforces which act on the endoprosthesis.

[0017] A medium may be present between the inner wall and the outerwall, by which an externally applied pressure is uniformly distributedto all sides. For example, when using a fluid as the medium, a forceacting on the inner wall of the receptacle, in particular a local orpoint force, is uniformly distributed in the receptacle. Local loadpeaks at the interface between the outer wall and the bone or cement areavoided. Preferably, the medium is composed such that it possesses theproperties of damping and pressure distribution.

[0018] The present invention therefore provides a durable, stableanchoring of an endoprosthesis in a bone, because the previous rigidconnection between the shaft and the bone or cement is avoided. Theobject underlying the invention is therefore completely achieved.

[0019] In a preferred embodiment, the inner wall comprises a slightelastic movability.

[0020] The feature has the advantage that the impact forces acting onthe endoprosthesis are already pre-dampened by the inner wall. Slightlyelastically movable will be understood in that the freedom of movementof the endoprosthesis is not substantially larger than if theendoprosthesis -were implanted in the bone without the quiver-likereceptacle, i.e. the endoprosthesis is not float-mounted in thereceptacle, but is securely anchored. The momentum transfer to themedium resulting from an elastic movement of the inner wall is damped bythe medium and/or uniformly distributed in the medium.

[0021] In a further preferred embodiment, the outer wall is configuredto be rigid.

[0022] The feature has the advantage that the outer wall provides asecure anchoring of the receptacle and thus the endoprosthesis in thebone.

[0023] In a further preferred embodiment, the inner wall and/or themedium has a form memory.

[0024] The feature has the advantage that the inner wall always returnsto its original form after an elastic movement due to a force acting onthe endoprosthesis shaft, so that the endoprosthesis does not shift withtime with respect to the bone in which it is implanted.

[0025] In a further preferred embodiment, additional walls are formed inthe space between the inner wall and the outer wall, which are connectedto the inner wall and the outer wall and subdivide the space into two ormore chambers.

[0026] The additional walls contribute in advantageous manner to theincreased stability of the quiver-like receptacle.

[0027] Preferably, the additional walls are elastically movable.

[0028] The feature has the advantage that the further walls contributeto the dampening of shocks or impacts in addition to the medium, wherebythe effect of the receptacle as a shock absorber is further improved.

[0029] In a further preferred embodiment, the medium comprises a liquid.

[0030] A liquid as the medium advantageously produces a uniformdistribution to all sides of a pressure exerted by the shaft on theinner wall. The further advantage is that regardless of the direction ofthe force acting on the shaft of the endoprosthesis, a pressure isdirected towards all sides perpendicular to the outer wall and the innerwall. No forces act on the outer wall parallel to the bone tissuesurface. Thus a slipping or rubbing of the outer wall with respect tothe surface of the bone tissue is avoided.

[0031] A further advantage of a liquid is that an increased pressureinstantaneously arises even with a small volume reduction of the spacebetween the inner wall and the outer wall due to an impact on theendoprosthesis. The increased pressure also acts on the inner wall ofthe receptacle and the receptacle is then forced more securely againstthe shaft of the endoprosthesis. The device thus becomesself-stabilising. A liquid with a high coefficient of friction ispreferred, because such a liquid is capable of dissipating kineticenergy through friction.

[0032] In a further preferred embodiment, the medium comprises a gas.

[0033] The use of a gas as the medium has the advantage that it has theproperty of compressibility. With a corresponding prepressurisation ofthe gas in the space between the inner wall and the outer wall, adampening of impact forces is produced by a lesser or greater increasein pressure depending on the prepressurisation of the gas. A uniformpressure distribution to all sides is provided in a gas, as in a liquid.

[0034] In a further preferred embodiment, the medium is a highlyviscous, elastically deformable mass or a solid material having anelastic compressibility.

[0035] The mentioned substances represent further advantageous examplesof a medium, which is suited to dampen impact forces through dissipationor to cause a uniform pressure distribution in the space between theinner wall and the outer wall.

[0036] In a further preferred embodiment, a portion of the inner wallsupporting a distal end of the shaft comprises a reinforcement.

[0037] This feature has the advantage that this region of the inner wallcan withstand high loads over long duration, since most of the impactforces acting on the endoprosthesis are directed vertically downwardlyand are transferred from the lower end of the shaft to this region ofthe inner wall lying below.

[0038] In a further preferred embodiment, the inner wall consists of amaterial containing a rubber mixture of high hardness. This feature hasthe advantage that the inner wall has a slightly elastic movability andon the other hand a sufficiently high rigidity and wear resistance.

[0039] In a further preferred embodiment, the inner wall comprises ametal mesh.

[0040] The feature has the advantage that the inner wall is configuredwith sufficiently high strength, in particular tear resistance, where onthe other hand, a mesh structure still allows a sufficiently elasticmovability of the inner wall. In particular, the metal mesh can still becoated with the mentioned high strength rubber mixture or a comparablecoating.

[0041] In a further preferred embodiment, the outer wall consists ofmetal.

[0042] The feature has the advantage that the outer wall can be producedwith sufficiently high strength and rigidity to achieve a secureanchoring of the receptacle in the bone.

[0043] In a further preferred embodiment, the medium is prepressurised.

[0044] The feature has the advantage that the damping characteristic ofthe quiver-like receptacle can be variably adjusted by the correspondingpressurisation. It is thus possible to adapt the damping characteristicof the receptacle to the osteological, anatomical conditions of theindividual patient.

[0045] Preferably, the medium is prepressurised by inserting the shaftinto the receptacle.

[0046] The feature has the advantage of achieving pressurisation in themedium in simple manner. For example, when using a liquid or gas as themedium, this can be accomplished in that the inner diameter of thereceptacle when the shaft is not inserted is smaller than the outerdiameter of the shaft. A volume reduction in the space between the innerwall and the outer wall of the receptacle results when inserting theshaft into the receptacle, which then leads to an increase in pressurein the space. The shaft is also securely held in the receptacle in atype of press-fitting.

[0047] In a further preferred embodiment, the prepressurisation isadapted to the hardness of the bone.

[0048] The feature has the advantage that the elasticity properties ofthe receptacle on the whole can be adjusted such that they correspond tothe elasticity of the bone.

[0049] In a further preferred embodiment, a contour of the outer wall ofthe receptacle is adapted to a predetermined contour of an implantationregion in the bone.

[0050] This feature is of particular advantage when the implantationregion in the bone, for example the marrow cavity in the femur, cannotbe be preprepared to form a uniform and flat bone tissue surface due tostrong deterioration or due to a complicated fracture.

[0051] In a further preferred embodiment, a stent for receiving thereceptacle is additionally provided, which can be implanted in the bone.

[0052] The feature has the advantage that the placement of thearrangement comprising the shaft and quiver-like receptacle in the boneis simplified. For implantation of the endoprosthesis the stent, whichadvantageously can be self-expandable, is placed in contracted conditionin the bone, for example in a previously prepared marrow cavity. It isthen released and expands to lie adjacent to the bone surface. Thearrangement comprising the endoprosthesis and the quiver-like receptaclecan then be inserted into the stent.

[0053] In a further preferred embodiment, the endoprosthesis is securedto the outer wall against vertical tensile forces by a tension anchor.

[0054] The feature has the advantage that a withdrawal of theendoprosthesis from the receptacle is reliably avoided when a tensileforce is present in the hip region. The tension anchor canadvantageously be an elastic cable with small elongation or a chain, tobe able to dampen peak loads of tensile force.

[0055] In a further preferred embodiment, a bottom portion of the outerwall of the receptacle comprises an elastic shock absorbing element.

[0056] The feature has the further advantage that particularly hardimpacts or shocks acting on the endoprosthesis are absorbed and dampedwhen the endoprosthesis is forced downwardly.

[0057] In a further preferred embodiment, the device comprises means forfixing the endoprosthesis in the receptacle against rotation.

[0058] The feature has the further particular advantage that theendoprosthesis is secured in the receptacle against rotation caused bytorques acting on the endoprosthesis. This is of particular importancebecause such endoprostheses generally are not rotationally symmetricalwith respect to the axis of the shaft, and the neck of theendoprosthesis extends at an angle from the shaft. A securement againstrotation according to the invention therefore has the advantage that theangular orientation of the endoprosthesis provided at the time ofimplantation remains unchanged.

[0059] Preferably, the means for fixing against rotation have propertiesfor damping rotation.

[0060] The feature has the advantage that torques acting as impacts orshort pulses on the endoprosthesis can be elastically dampened.

[0061] In a further preferred embodiment, the means for fixing theendoprosthesis against rotation comprise at least one strip elementextending between the outer wall and the inner wall in axial directionof the receptacle and at least one rigid rib engaging the strip element,which is fixidly secured to the shaft of the endoprosthesis.

[0062] Of advantage is that a securement against rotation of theendoprosthesis in the receptacle is achieved by technically simplemeans.

[0063] In addition, the strip element is preferably made of hard rubberor is configured as a hollow body filled with a polymer fluid of highviscosity.

[0064] In this embodiment of at least one strip element, a securementagainst rotation is provided in anchoring the endoprosthesis and on theother hand, rotational damping properties are provided.

[0065] In a further preferred embodiment, the means for fixing againstrotation comprise two diametrically opposite strip elements.

[0066] A reliable securement against rotation of the endoprosthesis isachieved by the simple construction of two diametrically opposite stripelements.

[0067] In a further preferred embodiment, the at least one strip elementextends from about the upper end of the inner wall to the lower end ofthe inner wall.

[0068] A particularly stable and twist-free securement against rotationis advantageously achieved with this feature. With the provision thatthe at least one strip element extends only to the lower end of theinner wall, it is achieved that the medium located between the innerwall and the outer wall can still uniformly distribute and dampen animpact on the endoprosthesis throughout the entire space between theinner wall and the outer wall.

[0069] In a further preferred embodiment, the inner wall of thereceptacle is not round in cross-section and the shaft of theendoprosthesis has a complementary cross-section thereto.

[0070] A securement against rotation of the endoprosthesis in thereceptacle is achieved by constructively simple means through thisconfiguration of the inner wall of the receptacle and the shaft.

[0071] In further preferred embodiments, the mentioned cross-section isapproximately oval or approximately rectangular.

[0072] These forms of the cross-section can be manufactured inadvantageous manner with little technical complexity both for the innerwall of the receptacle and for the endoprosthesis.

[0073] In a further preferred embodiment, the outer wall of thereceptacle is not round in cross-section.

[0074] The feature has the considerable advantage that the receptacleitself is secured against rotation in the femur. Preferably, thecross-section is approximately rectangular.

[0075] Further advantages will become apparent from the followingdescription and the attached drawings. It will be understood that theabove-mentioned features and those to be discussed below are not onlyapplicable in the given combinations, but may also be taken in othercombinations or alone without departing from the scope of the presentinvention.

[0076] Embodiments of the invention are illustrated in the drawings andare discussed in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077]FIG. 1 shows a device for anchoring an endoprosthesis in a femurin longitudinal cross-section according to a first embodiment.

[0078]FIG. 2 shows a device for anchoring the endoprosthesis of FIG. 1in a femur in longitudinal cross-section according to a secondembodiment of the present invention.

[0079]FIG. 3 shows a cross-section of the anchoring of an endoprosthesisaccording to a third embodiment, where the endoprosthesis is not shown.

[0080]FIG. 4 shows a cross-section through the device of FIG. 3 alongthe line IV-IV in FIG. 3.

[0081]FIG. 5 shows a perspective view of a central section of a furtherembodiment of the device for anchoring an endoprosthesis in the femur.

[0082]FIG. 6 shows a cross-section along the line VI-VI in FIG. 5.

[0083]FIG. 7 shows a further embodiment of a device for anchoring anendoprosthesis in the femur in an illustration corresponding to FIG. 6.

[0084]FIG. 8 shows a further embodiment of a device for anchoring anendoprosthesis in the femur in an illustration corresponding to FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0085]FIG. 1 shows a device for anchoring an endoprosthesis 12 in a bone14 generally indicated by the numeral 10. The illustrated embodimentrepresents the endoprosthesis 12 as the thigh portion 16 of a hip jointprosthesis which is implanted in the femur 18 of a patient.

[0086] The thigh portion 16 comprises a ball 20 at its upper end, whichcorresponds to the ball joint in the hip of a healthy human. A neck 22extends below the ball 20, which is followed by a shaft 24. The neck 22is angled with respect to the shaft 24, where the ball 20 is arranged tothe side of the centre axis of the shaft 24. Thus the position of theball 20 of the thigh portion 16 corresponds to the anatomical positionand orientation of the ball joint of the human hip. In the implantedcondition, the neck 22 and the ball 20 project from the femur 18.

[0087] The ball 20, the neck 22 and the shaft 24 are integrally formedas one piece and are made massively of a metal suitable for medicalpurposes. The shaft 24 as seen in FIG. 1 is cylindrical. The presentinvention however is not limited to a cylindrical form of the shaft 24,but is applicable for other endoprostheses. Other endoprostheses mayhave a shaft extending downwardly to form a tip or may have a shaftwhich tapers to form a truncated cone, which in addition may also have acurved form.

[0088] The materials for the endoprosthesis 12 can be selected fromCo—Cr alloys, V4A steel and ceramic or titanium alloys, for exampleTi₆Al₄V.

[0089] The device 10 is configured in the form of a quiver-likereceptacle 26 in which the shaft 24 of the thigh portion 16 is received.The receptacle 26 is placed in a bone marrow cavity 28 of the femur 18,where the region of the cavity in which the receptacle 26 is insertedhas been operatively prepared beforehand. A conically tapered stopper 30is placed in the cavity 28 before inserting the receptacle 26, whichprevents a deeper penetration of the receptacle 26 into the cavity 28.The receptacle 26 is implanted in the cavity 28 with cement or free ofcement.

[0090] The receptacle 26 is open to the top, so that the shaft 24 can beinserted in the receptacle 26 from the top. The receptacle comprises aninner wall 32, which is formed cylindrically as is the shaft 24 andwhich completely surrounds the shaft 24. The inner wall 32 has aU-shaped cross-section.

[0091] The receptacle 26 further comprises an outer wall 34 which whenplaced in the cavity 28 lies adjacent to the bone tissue of the femur 18or, when cemented, adjacent to the cement mantle. The inner wall 32 andthe outer wall 34 are securely and tightly connected to one another atthe upper end 40 of the receptacle 26, where the turned over region 42still belongs to the inner wall 32.

[0092] The inner wall 32 and the outer wall 34 define a base or bottomportion 36 as well as a leg portion 38 of the receptacle 26. In theregion of the base portion 36, the outer wall 34 is further spaced fromthe inner wall 32 than in the region of the shank portion 38.

[0093] The inner wall 32 has a slightly elastic movability and consistsof a material containing a high strength rubber mixture, where a metalnet or mesh is embedded in the rubber mixture. In contrast, the outerwall 34 is rigidly formed of a metal. The outer wall 34 has the form ofa cylinder closed at the bottom. The inner wall 32 also has acylindrical contour.

[0094] A space 44 between the inner wall and the outer wall is filledwith a medium 45, which is capable of damping impacts and/or is capableof uniformly distributing a pressure applied externally to substantiallyall sides. In the embodiment shown in FIG. 1, the space 44 ishermetically sealed by the inner wall 32 and the outer wall 34 and iscompletely filled with a liquid, for example a 0.9% saline solution.Other bio-compatible inert liquids can be employed, in particular thosewith a high inner coefficient of friction.

[0095] Instead of a liquid, the space 44 can also be filled with a gaswhich is provided in the space 44 with an over-pressure and depending onthe given fill pressure has a certain compressibility.

[0096] A highly viscous elastically deformable mass or a solid substancehaving an elastic compressibility can also be placed in the space 44.The latter substances represent media which are capable of dissipatingand therefore dampening mechanical energy applied in the form of impactsor kinetic energy applied variably. In addition, these substances havethe ability to uniformly distribute pressure in substantially alldirections.

[0097] The inner wall 32 and/or the medium 45 in the space 44 also havethe property of form memory, such that a deformation of the receptacle26 at the inner wall 32 due to an impact acting on the shaft does notremain as a deformation of the inner wall 32 or the medium 45. Rather,these elements always return to their previous form and position. Inother words, the inner wall 32 and the medium 45 in the space 44comprise a form stability due to the elastic recovery forces, withoutthe inner wall 32 or the medium 45 having a spring effect.

[0098] A section 46 of the inner wall 32 for supporting the lower end ofthe shaft 24 has a reinforcement, where the reinforcement is configuredsuch that the inner wall 32 in this region is provided with a greaterthickness. A rigid plate of synthetic material or metal can also beprovided in the section 46.

[0099] To implant the endoprosthesis 12, the endoprosthesis 12 isinitially placed in the quiver-like receptacle 46 outside of the humanbody. The receptacle 26 is configured such that the clearance innerdiameter of the receptacle 26 when the endoprosthesis 12 is not insertedis smaller than the outer diameter of the shaft 24. When inserting theshaft 24 in the receptacle 26, the inner wall 32 is compressed by theshaft 24 on all sides, where the volume of the space 44 is reduced. Themedium contained in the space 44, for example the liquid, the gas, thehighly viscous elastic mass or the elastically compressible solid isprepressurised, whereby the inner wall 32 is securely joined to theshaft 24 and the shaft 24 is seated in the receptacle 26 without play.

[0100] Subsequently, the arrangement including the endoprosthesis 12 andthe receptacle 26 are placed in the bone marrow cavity 24 of the femur18.

[0101] The effect of the device 10 will now be described when a load isapplied to the endoprosthesis 12, for example a shock or impact. When aforce F₁ acts on the endoprosthesis 12, such as a vertical forceillustrated in FIG. 1, the lower end of the shaft 24 acts as a stampingmeans which exerts a pressure in the direction of the arrow 48 on themedium in the space 44 in the region of the base portion 36 of thereceptacle 26. A small portion of the medium 45 is displaced out of thebase portion 36 into the leg portion 38 as indicated by the arrows 49.The medium in the space 44 now causes the pressure pulse from the baseportion 36 to be uniformly distributed to substantially all sides and/orto be dampened by the medium.

[0102] When the medium in the space 44 is a liquid, for example a salinesolution, the effect is mainly that the pressure exerted by the shaft 24caused by the force F is uniformly distributed in the base portion 36and the shank portion 38 of the receptacle 26. The pressure alwaysremains perpendicular to the inner wall 32 and the outer wall 34 asindicated by the arrows 50 and 51. Through the uniform distribution ofthe pressure, an excessive local or point load at an interface, forexample indicated by the numeral 52, is avoided. Such an excessive loadcan be caused for example by a force indicated by F₂, which causes aninterface overload between the outer wall 34 and the bone tissue of thebone 14.

[0103] A damping of the force or impact exerted by the shaft onto theinner wall 32 can be achieved with a medium which is capable ofirreversibly transforming kinetic energy into heat due to the high innerfriction of the medium. Such media for example are highly viscousliquids or masses.

[0104] The forces acting on the inner wall 32 of the receptacle 26 asindicated by the arrows 51 also produce a stabilisation of the shaft 24in the receptacle 26. The device 10 therefore is self-stabilising.

[0105] Furthermore, the endoprosthesis 12 is secured against verticallyupwardly directed forces on the receptacle 26 by a tension anchor 54.The tension anchor 54 is formed by an elastic cable or an elastic chain,whose one end is secured at the lower end of the shaft 24 of theendoprosthesis 12 and whose other end is secured at a bottom section 58of the outer wall 34 of the receptacle 26. The tension anchor 54prevents the endoprosthesis 12 from being drawn out of the receptacle 26by tensile forces.

[0106] The bottom section 58 of the outer wall 34 of the receptacle 26is also provided with an elastic shock absorbing element 56, whichabsorbs an impact on the endoprosthesis causing it to be pusheddownwardly.

[0107] A second embodiment of a device for anchoring the endoprosthesis12 in a bone 62 is shown in FIG. 2 and generally designated by thenumeral 60. The tissue surface 64 of the bone marrow cavity 66 of thebone 62 has a disrupted structure. In such an application, where thedisrupted structure of the tissue surface 64 can no longer bepreprepared to form a uniform tissue surface, a quiver-like receptacle68 is provided whose contour at an outer wall 70 of the receptacle 68 isadapted to the disrupted contour of the tissue surface 64 of the bone62. The outer wall 70 can be fabricated on the basis of data obtained bycomputer tomography or obtained by means of conventional X-ray images.

[0108] In addition, a stent 72 is provided in the device 60 of FIG. 2,into which the receptacle 70 is inserted. The stent 72 comprises abottom 74 and a peripheral outer wall 76, whereby the outer wall 76 alsois adapted to the contour of the tissue surface 64. Such stents can alsobe used in the device 10 shown in FIG. 1, where in that case, the stenthas a cylindrical form. The stent is preferably self-expandable.

[0109] When using a stent in addition to the quiver-like receptacle 26or 68, the stent is initially inserted into the bone marrow cavity 28 or66, where the arrangement comprising the endoprosthesis 12 and thequiver-like receptacle 26 or 68 is then inserted into the stent.

[0110]FIGS. 3 and 4 illustrate a further embodiment of a device 80 foranchoring an endoprosthesis (not shown in FIGS. 3 and 4) in a bone,which is also not shown. A quiver-like receptacle 82 differs from thereceptacle 26 in FIG. 1 in that further walls 88, 90 are providedbetween the inner wall 84 and the outer wall 86. The further walls 88are connected to the inner wall 84 and the outer wall 86. The walls 88are illustrated here as horizontally arranged rings, while the wall 90runs vertically in the base portion 92 of the receptacle 82 between theouter wall 86 and the inner wall 84.

[0111] The walls 88 and 90 are elastically displaceable. The walls 88and 90 subdivide a space 94 between the inner wall 84 and the outer wall86 into a number of chambers 96, where in the example of FIG. 3 a totalof six chambers are present. The walls 88 and 90 can also be configuredsuch that a medium 98 present in the space 94 can be transferred fromone chamber to another. This can be accomplished for example byproviding a small opening in the walls 88 or 90.

[0112] The quiver-like receptacles 26, 68, 82 can be implanted withoutcement or can be implanted with cement in the bones 14, 62.

[0113] A further embodiment is shown in FIGS. 5 and 6 and illustrated asa device 100 for anchoring an endoprosthesis in the femur 18. Only acentral axial section of the device 100 is shown in FIG. 5 as well as ashaft 104 of the endoprosthesis 102. The femur 18 is not illustrated inFIG. 5.

[0114] The device 100 is also configured in the form of a quiver-likereceptacle 106, which as in the previous embodiments comprises an innerwall 108 and an outer wall 110. The receptacle 106 is also filled with amedium 112 between the inner wall 108 and the outer wall 110. The mediumdampens impacts and/or uniformly distributes an externally appliedpressure substantially to all sides, as described above in detail.

[0115] In addition, the quiver-like receptacle 106 comprises furtherwalls 114 and 116 interconnecting the inner wall 108 and the outer wall110, which are axially displaced from one another. Two such walls areillustrated in FIG. 5. The walls 114 and 116 run approximatelyhorizontally and subdivide the space between the inner wall 108 and theouter wall 110 into several chambers 118, 120. Each of the walls 114,116 comprises openings 122, 124 through which the medium 112 cancommunicate between the neighbouring chambers 118, 120 as indicated withthe arrow 126.

[0116] The device 100 also comprises means 128 for fixing theendoprosthesis 102 against rotation in the receptacle 106. The means 128for fixing the endoprosthesis 102 against rotation comprise two stripelements 130 extending between the inner wall 108 and the outer wall 110in longitudinal direction of the receptacle 106. The two strip elements130, 132 are arranged to be diametrically opposed.

[0117] The strip elements 130, 132 in cross-section form approximately asector of a circle and extend in axial direction from the upper end (notshown in FIG. 5) of the inner wall 108 to the lower end of the innerwall 108 and pass through the horizontal walls 114, 116. Since the stripelements 130, 132 only extend to the lower end of the inner wall 108,the entire space between the inner wall 108 and the outer wall 110 forma continuous volume for the medium 112 corresponding to the embodimentsof FIGS. 1 to 4. The strip element 130 and the strip element 132 consistof hard rubber or are formed as hollow bodies filled with a highlyviscous polymer liquid.

[0118] The strip element 130 engages with a rigid rib 134 extendingradially outwardly from the shaft 104 of the endoprosthesis 102 andextending axially over the shaft 104. The rib is fixedly connected tothe shaft 104 of the endoprosthesis 102. The rib 134 is formed togetherwith the shaft 104 or is welded to the shaft 104. A rib 136diametrically opposed to the rib 134 also engages with the strip element132.

[0119] The endoprosthesis 102 is thus secured in the receptacle 106against rotation caused by rotary forces being applied to the device.Due to the constitution of the strip element 130 of a hard elasticmaterial, such as hard rubber, the fixation is not completely stiff, buthas properties of damping the rotation. In this manner, sudden torquesapplied to the endoprosthesis are dampened by the fixation againstrotation.

[0120] As a further embodiment of the invention, a device 140 is shownin FIG. 7 for anchoring an endoprosthesis 142 in the femur 18, whichdiffers from the embodiment of FIGS. 5 and 6 in the geometricalconfiguration of an inner wall 144 and an outer wall 146 of aquiver-like receptacle 148 in which a shaft 150 of the endoprosthesis142 is received. The inner wall 144 has an approximately ovalcross-section, where the shaft 150 of the endoprosthesis 142 has acorresponding cross-sectional form adapted in form-locking manner to theform of the inner wall 144.

[0121] The outer wall 146 has an approximately rectangular form. Thereceptacle 148 thus secures itself in the femur 18 against rotation. Inaddition, the device 140 comprises means 152 for fixing theendoprosthesis 142 against rotation in the receptacle 148. The means 128correspond to those of the embodiment in FIGS. 5 and 6 and are thereforenot described in more detail here.

[0122] As can also be taken from FIG. 7, the bone marrow cavity 28 ofthe femur 18 has not been prepared corresponding to the geometry of theouter wall 146 with a rectangular cross-section, but still has a roundedcross-section. The receptacle 148 penetrates with its corners into thefemur 18 for reliable anchoring in the femur 18. It can be expected thattissue will grow with time in the free intermediate space between theouter wall 146 of the receptacle 148 and the femur 18, which then willcompletely cover the outer wall 146 of the receptacle 148. The cornersof the outer wall 146 can also be rounded instead of the strict rightangle geometry of the outer wall 146 shown in FIG. 7.

[0123] Finally, a further embodiment of a device 160 for anchoring anendoprosthesis 162 in the femur 18 is shown in FIG. 8. The device 160also comprises means 165 for fixing the endoprosthesis 162 againstrotation in constructively very simple manner.

[0124] In contrast to the above embodiment, the device 160 is configuredin the form of a quiver-like receptacle 164, whose inner wall 166 aswell as an outer wall 168 is configured to be rectangular incross-section. A shaft 174 of the endoprosthesis 162 correspondinglycomprises a rectangular geometry in cross-section. With thisconfiguration of the shaft 174 of the endoprosthesis 162 and the innerwall 166 of the receptacle 164, the endoprosthesis 162 is alreadyanchored to be fixed against rotation in the receptacle 164, withoutadditional measures needing to be taken.

[0125] As in the previous embodiments, the receptacle 164 includesapproximately horizontally disposed walls 170 interconnecting the innerwall 166 and the outer wall 168. The walls 170 comprise four openings172 for passage of a medium 176, which can then communicate between thechambers formed by the walls 170.

[0126] The respective walls 170 are formed with correspondingly elasticproperties to achieve rotational damping of the endoprosthesis 162 inthe receptacle 164.

[0127] It will be understood that the present invention, described abovein conjunction with embodiments relating to the thigh portion of a hipjoint prosthesis, can also be employed for the pelvic portion of a hipjoint endoprosthesis or for a knee joint endoprosthesis or forendoprostheses for other large joints. It will be also understood thatthe features of the different embodiments can be combined with oneanother, for example a tension anchor according to FIG. 1 can beprovided in the embodiments of FIGS. 5 to 8 or a securement againstrotation of the endoprosthesis in FIGS. 5 to 8 can be provided in thedevice of FIG. 1. In addition, a stent can be provided in all of theembodiments, in which the quiver-like receptacle is received.

What is claimed is:
 1. A device for anchoring an endoprosthesis in abone, for example a thigh part of a hip joint endoprosthesis in a femur,wherein said device is configured in form of a quiver-like receptacleimplantable in said bone for receiving a shaft of said endoprosthesis,said receptacle comprising: an inner wall enclosing said shaft, an outerwall disposed at a distance from said inner wall, a medium filled in aspace between said inner wall and said outer wall, in which medium anexternally applied pressure is uniformly distributed substantially toall sides for damping impacts exerted on said endoprosthesis, whereinsaid inner wall is disposed at a distance from said outer wall also at adistal most end of said receptacle.
 2. The device of claim 1 , whereinsaid inner wall comprises a slight elastic movability.
 3. The device ofclaim 1 , wherein said outer wall is configured to be rigid.
 4. Thedevice of claim 1 , wherein at least one of said inner wall and saidmedium has a form memory.
 5. The device of claim 1 , wherein furtherwalls are formed in said space between said inner wall and said outerwall, which are connected to said inner wall and said outer wall andsubdivide said space in at least two chambers.
 6. The device of claim 5, wherein said further walls are elastically movable.
 7. The device ofclaim 1 , wherein said medium comprises a liquid.
 8. The device of claim1 , wherein said medium comprises a gas.
 9. The device of claim 1 ,wherein said medium comprises a highly viscous elastically deformablemass or a solid material having an elastic compressibility.
 10. Thedevice of claim 1 , wherein a portion of said inner wall supporting adistal end of said shaft comprises a reinforcement.
 11. The device ofclaim 1 , wherein said inner wall consists of a material containing arubber mixture of high hardness.
 12. The device of claim 1 , whereinsaid inner wall comprises a metal mesh.
 13. The device of claim 1 ,wherein said outer wall consists of a metal.
 14. The device of claim 1 ,wherein said medium is prepressurised.
 15. The device of claim 14 ,wherein said medium is prepressurised by inserting said shaft into saidreceptacle.
 16. The device of claim 1 , wherein said medium isprepressurised and said prepressurisation is adapted to the hardness ofsaid bone.
 17. The device of claim 1 , wherein a contour of said outerwall of said receptacle is adapted to a predetermined contour of animplantation region of said bone.
 18. The device of claim 1 , wherein astent is additionally provided for receiving said receptacle, which canbe implanted in said bone.
 19. The device of claim 1 , wherein saidendoprosthesis is secured against vertical tensile forces by a tensionanchor on said outer wall.
 20. The device of claim 1 , wherein a bottomportion of said outer wall of said receptacle comprises an elastic shockabsorbing element.
 21. The device of claim 1 , wherein said devicecomprises means for fixing said endoprosthesis against rotation in saidreceptacle.
 22. The device of claim 21 , wherein said means for fixingagainst rotation comprise properties of dampening rotation.
 23. Thedevice of claim 1 , wherein said device comprises means for fixing saidendoprosthesis against rotation in said receptacle and wherein saidmeans for fixing said endoprosthesis against rotation comprise at leastone strip element extending between said outer wall and said inner wallin axial direction of said receptacle and at least one rigid rib whichengages in said strip element and is fixedly seated on said shaft ofsaid endoprosthesis.
 24. The device of claim 23 , wherein said stripelement consists of hard rubber or is formed as a hollow body filledwith a highly viscous polymer fluid.
 25. The device of claim 1 , whereinsaid device comprises means for fixing said endoprosthesis againstrotation in said receptacle and wherein said means for fixing againstrotation comprises two strip elements diametrically opposite to oneanother.
 26. The device of claim 24 , wherein said at least one stripelement extends approximately from an upper end of said inner wall to adistal end of said inner wall.
 27. The device of claim 1 , wherein saiddevice comprises means for fixing said endoprosthesis against rotationin said receptacle and wherein said inner wall of said receptacle is notround in cross-section and said shaft of said endoprosthesis comprises across-section complementary thereto.
 28. The device of claim 27 ,wherein said cross-section is approximately oval or approximatelyrectangular.
 29. The device of claim 1 , wherein said outer wall of saidreceptacle is not round in cross-section.
 30. The device of claim 29 ,wherein said cross-section is approximately rectangular.